Jean-Charles Delvenne Vincent D. Blondel Quasi-periodic configurations and undecidable dynamics for tilings, infinite words and Turing machines. 127-143 2004 319 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2004.02.018 db/journals/tcs/tcs319.html#DelvenneB04